In a track-type machine or crawler tractor, such as a bulldozer, an endless track is formed from a plurality of track shoes carried by links which are pivotably connected by means of hinged pins and bushings. Normally, at least one link assembly, the "master track link" assembly, is constructed to be separable or detachable thereby enabling the endless track to be mounted on or removed from the tractor or machine to which it is attached.
Master track link connections or assemblies commonly comprise two link parts, each adapted to receive a pin and each having a mating surface to interlock with the mating surface of the other link part or half. Preferably, the master track link should provide a connection which is simple enough to permit servicing of the assembled track in the field without having to use special tools. The master track link, of course, should be strong enough to stand up under the stresses experienced during the operation of the machine to which it is attached. Each interconnected link assembly is subject to extremely high tensile and compressive forces resulting from the driving engagement of the sprocket wheels and the hinge joints. It is also desirable to provide master link parts or halves which are easily machined and which facilitate assembly and disassembly of the track link. This is particularly desirable on large machines having relatively heavy endless track assemblies and which, more often than not, must be repaired in the field. Thus, master track links must be both durable and convenient to service if costly down time is to be minimized.
The outer surface of the master track link, like the other links, carries a track shoe. The shoe is joined to the two halves of the master track link by means of shoe bolts or track bolts. Normally, these shoe bolts have a relatively long threaded length to reduce thread fatigue and stress. Experience has shown that master track links formed from half links which are held together by pins or toothed keys reduce the stress imposed upon the shoe bolts. By keeping the stresses on the shoe bolts relatively low, they will not have a tendency to break thereby dislodging or loosening the associated track shoe. Thus, an interlocking, two-piece, master track link has a longer operating life.
Two-piece interlocking master track links have been disclosed. Typical examples are found in U.S. Pat. No. 4,050,750 to Yoshihashi; U.S. Pat. No. 3,427,079 to Skromme; U.S. Pat. No. 3,822,923 to Stedman; and U.S. Pat. No. 3,020,096 to Strand. Heretofore, relatively close tolerances have been required to assure optimum coupling of the two interlocking surfaces and alignment of the shoe bolts joining together the two link parts. If the tolerances are relaxed too far, the two halves of the master track link can come out of alignment. This increases the localized stresses to the point that damage soon results. Track links having relatively close tolerances are costly. An excessive amount of custom fit-up is often required. If the interface between the two master track link parts is too imperfect, dirt or other corrosive materials can be worked into the gaps and cavities in the interface. This accelerates localized corrosion and complicates the removal of the two master track link parts when they must be serviced or repaired.
From the foregoing it should be appreciated that master track link design still leaves room for improvement. An improved track link should distribute the tensile load exerted upon the two halves of the master track link more broadly across the mating surfaces of the link parts to prevent localized stress therein. This would also reduce the load on the shoe bolts. An interfacing surface which can be readily or easily machined and aligned would go far towards minimizing localized corrosion and improving the repairability of the master track link. If the load on the track bolts or shoe bolts could be reduced, there would be less tendency for the shoe bolts to break or fail under load. Finally, a master track link design which is relatively compact and which has a relatively small mating surface or area would have a lower fabrication cost. Ideally, this cost advantage should be gained without compromising the inherent strength of the master link.